This invention relates to a method for providing, from a variety of product sources, including a bulk supply, a continuous double discharge of discrete quantities of product, with each quantity having a predetermined target weight, or a weight very close thereto. This is accomplished by dividing the source product into a plurality of smaller quantities that are a fraction of the target weight. Each of the fractional weight quantities becomes part of a set for which all possible double discharge fractional weight combinations are determined. A combination providing two discharges of the target weight, or of the preferred weight closest to the target weight, is selected. In many instances the preferred weight is that weight closest to but not less than the target weight; other criteria for selecting the preferred weight are possible. The selected double discharge fractional weight combination is then split into two acceptable discharges of discrete quantities of product. Electrical circuitry may be used to determine the possible weight combinations and select the combination providing the preferred weight.
Such method of achieving a desired weight of flowing product, as is disclosed and claimed in this application, is novel and provides a machine cycle rate which is more efficient and quicker than that previously provided by weighing machines.
As used herein, "package weight" is the actual weight of product which a weighing machine provides per package on any single machine cycle, "double product weight" is the actual weight of product which the weighing machine provides on any single machine cycle and is approximately twice the package weight, "target weight" is the weight of product which the user desires the weighing machine to provide per package on any single machine cycle, "fractional weight" is the weight of a fractional weight quantity available on any single machine cycle, "preferred product weight" is that combination of fractional weights which the user desires the weighing machine to use to make up the package weight on any single machine cycle, and an "acceptable weight" is a combination of fractional weights which results in a package weight within a range of weights predetermined by the user. As mentioned, the preferred weight is often defined as that combination of fractional weights which is closest to but not less than the target weight, but other criteria are possible. An acceptable weight is correspondingly often defined as a weight which is greater than the target weight but less than a known weight in excess of the target weight, but other criteria for this term are also possible.
In the past, weighing machines have been slow, inaccurate, expensive, and bulky. In addition, they have abused the product, failed to achieve acceptable weights, and suffered from reliability problems due to their complexity. In an effort to overcome such disadvantages, some recent weighing machines have used a series of bins or hoppers to collect product from a continuous product supply, such as a conveyor. Such machines convert the continuous product flow into a series of discrete product groups that are each deposited onto a scale and weighed. Preferably, each discrete product group weighs a fraction of the target weight so that a number of them must be combined to obtain the package weight. For instance, if target weight is 100 grams, the weighing machine might create ten discrete fractional weight groups, each having an arbitrary weight between approximately 10 grams and 30 grams. The machine considers the possible fractional weight combinations available by combining the discrete product groups and selecting the combination providing the preferred weight.
Such prior art weighers have utilized a circular scale arrangement and radial product feed. Product is supplied by a chimney or hopper feeding directly onto a central distribution cone. Not all product may be fed this way because it may fail to feed through the chimney or hopper, or it may be damaged by such a feed configuration. In other instances, product is supplied by a conveyor, which makes it difficult to match the linear discharge end thereof with the radial dispersion of the distribution cone. For instance, it is desirable for the product to discharge in a narrow stream onto the apex of the distribution cone, but this is difficult to achieve due to vagaries in product flow and the unique feeding characteristics of each product. Thus, some scales may be deprived of product or starved while others receive an excessive amount of product and are flooded. This adversely impacts the ability of the weigher to achieve satisfactory operation. When a scale is starved, it is effectively eliminated because it is empty and cannot contribute to the possible combinations available to attempt to make the target weight. When a scale is flooded, it reduces the number of additional discrete weights that may be added to attempt to meet the target weight, again reducing the possible combinations available in attempting to meet the target weight. If the flooding is severe it may overflow the scale or place a weight of product in the scale which exceeds the acceptable package weight, requiring manual intervention or shut-down. The incidence of such problems is greatly reduced with the present invention.
The apparatus used in the prior art to provide discrete weighted amounts of product usually require an excessive number of scales, which is unduly expensive, and do not utilize sufficient means to optimally regulate product flow to the scales. This can lead to an excess or insufficient amount of product in the scales. Such a condition reduces the number of combinations available from which to attempt to meet the target weight, thereby reducing the accuracy of the weighing machine. To a limited extent, this has been alleviated by increasing the number of scales, but this also escalates the cost, complexity, and size of the weigher.
It is known in such prior art apparatus to employ arithmetic means for selecting which combinations of discreet product groups will provide the preferred product weight. The most common selection logic is sequential; i.e., a final decision is made about the first discharge before a second discharge computation is made. Apparatus exemplifying the sequential selection process are described, for example, in U.S. Pat. Nos. 4,385,671; 4,396,078; 4,418,771; and 4,441,567. This approach has been known to limit packaging speed in cases where, having made a first discharge, no acceptable second discharge can be made without refilling the weighing scales.
The present invention effectively doubles machine output by computing two discharges simultaneously and thereby permitting the discharge of two packages for each scale cycle; without adversely affecting the accuracy of the weigher. Moreover, each scale is used in each machine cycle, thus reducing the costs of the weigher apparatus and its operation.